Maybe they decided not to revisit that storyline after deciding the longterm goal for Kyle was to be an omnipotent hero. If he was going to be the carrier of the white light, harbinger of life, healer, giver of all that is good and awesome, bearer of goodness, titles, titles, titles...it would be very unseemly for him to go on a quest to get vengeance on Sinestro for murdering his mother. Even bringing him to justice on SOME level goes against where Kyle was heading (AND for where Sinestro was heading for that matter)...

Heh, I guess it would be a little inconsistent to simultaneously portray him as Space Jesus and Paul Kersey (Charles Bronson).

Geoff was writing the First Lantern story and I'm sure he had his hands in all of it as the CCO. So yeah, after Guy grew a 'stache and goatee and he was seen in the future with at least the 'stache... a brother was a tad bit worried Kyle's hair would get kinda long again and go the Space Jesus route.

Still waiting! A Kyle vs. Sinestro story with full stakes based on SINESTRO KILLING HIS FUCKING MOTHER sort of needs to happen at some point. Particularly now that there isn't a Geoff Johns around to FAKE remind DC that Sinestro needs to be superheroic... even though Sinestro killing Kyle's mom was literally his idea and he wrote it.